And then Marvel Studios has the added unction to not give as much cash since they're giving away free publicity to Sony's character, and there's definitely no guesstimate for how much Sony will receive extra on the next Spidey movie, and no creative control over it for Marvel. It's a bad deal from their end, afaik.

Marvel Studios has every incentive to give publicity to Sony's TASM. They have a very real vested interest in the success of the character. They own all of the merchandising, which is HUGE for them. Plus they still make a percentage, albeit probably small like 4-5%, of the box office. Bottom line is Sony is still a struggling production company and Disney/Marvel has several avenues to make money off of TASM. Both parties have something to gain from a partnership.